Author: Constantin Aniculaesei Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
This thesis describes experiments that explore the possibility of improving the quality of an electron beam obtained from a laser wakefield accelerator (LWFA) by shaping the longitudinal plasma density profile. Different density profiles have been obtained by employing a range of Laval nozzles with different geometries. These are modelled and numerically simulated under different conditions using Fluent 6.3. Density lineouts from simulations for different heights above the nozzle give the plasma density profile for each experimental condition. The plasma density profile is modified by changing the geometry of the nozzle, the interaction point, the laser beam angle relative to the exit plane of the nozzle and pressure of the gas. In this way the leading up-ramp length of the density profile (that interacts first with the laser) has been varied between 0.47 mm to 1.39 mm and the maximum plasma density varied between 1.29 x 1019 cm−3 to 2.03 x 1019 cm−3. The influence of the density profile parameters on the LWFA process is quantified by monitoring the properties of the generated electron beam. It is shown that the leading ramp of the plasma density profile i.e. the ramp that interacts first with the laser, has a strong influence on the quality of the electron beam. Density profiles with the same peak plasma density but different ramp lengths generate electron beams with a factor of 1.4 difference in charge, 1.1 in electron energy, 2 in pointing and 1.45 in energy spread. Longer ramp lengths enhance the quality of electron beams, which suggest that LWFA injection occurs at the entrance density ramp. Complex density profiles are produced by tilting the nozzle relative to the direction of propagation of the laser. This allows continuous tuning of the peak energy of the electron beam from 135 ± 2MeV up to 171 ± 2MeV. The electron beam energy spread show improvements from 20.7 ± 1.2% to 8.9 ± 0.9%. The charge closely follows the evolution of the energy spread and has a mean value of 0.61 ± 0.16 pC. Experimental results also show that the angular distribution of the electron beam becomes elliptical when the laser focal plane is moved from the edge of the gas jet towards the centre of the density profile. This result is linked to the existence of a distorted LWFA bubble that propagates off-axis therefore affecting the pointing and transverse shape of the electron beam.
Author: Karl Schmid Publisher: Springer Science & Business Media ISBN: 364219950X Category : Science Languages : en Pages : 169
Book Description
This thesis covers the few-cycle laser-driven acceleration of electrons in a laser-generated plasma. This process, known as laser wakefield acceleration (LWFA), relies on strongly driven plasma waves for the generation of accelerating gradients in the vicinity of several 100 GV/m, a value four orders of magnitude larger than that attainable by conventional accelerators. This thesis demonstrates that laser pulses with an ultrashort duration of 8 fs and a peak power of 6 TW allow the production of electron energies up to 50 MeV via LWFA. The special properties of laser accelerated electron pulses, namely the ultrashort pulse duration, the high brilliance, and the high charge density, open up new possibilities in many applications of these electron beams.
Author: Publisher: ISBN: Category : Languages : en Pages : 6
Book Description
Particle accelerators enable scientists to study the fundamental structure of the universe, but have become the largest and most expensive of scientific instruments. In this project, we advanced the science and technology of laser-plasma accelerators, which are thousands of times smaller and less expensive than their conventional counterparts. In a laser-plasma accelerator, a powerful laser pulse exerts light pressure on an ionized gas, or plasma, thereby driving an electron density wave, which resembles the wake behind a boat. Electrostatic fields within this plasma wake reach tens of billions of volts per meter, fields far stronger than ordinary non-plasma matter (such as the matter that a conventional accelerator is made of) can withstand. Under the right conditions, stray electrons from the surrounding plasma become trapped within these "wake-fields", surf them, and acquire energy much faster than is possible in a conventional accelerator. Laser-plasma accelerators thus might herald a new generation of compact, low-cost accelerators for future particle physics, x-ray and medical research. In this project, we made two major advances in the science of laser-plasma accelerators. The first of these was to accelerate electrons beyond 1 gigaelectronvolt (1 GeV) for the first time. In experimental results reported in Nature Communications in 2013, about 1 billion electrons were captured from a tenuous plasma (about 1/100 of atmosphere density) and accelerated to 2 GeV within about one inch, while maintaining less than 5% energy spread, and spreading out less than 1/2 milliradian (i.e. 1/2 millimeter per meter of travel). Low energy spread and high beam collimation are important for applications of accelerators as coherent x-ray sources or particle colliders. This advance was made possible by exploiting unique properties of the Texas Petawatt Laser, a powerful laser at the University of Texas at Austin that produces pulses of 150 femtoseconds (1 femtosecond is 10-15 seconds) in duration and 150 Joules in energy (equivalent to the muzzle energy of a small pistol bullet). This duration was well matched to the natural electron density oscillation period of plasma of 1/100 atmospheric density, enabling efficient excitation of a plasma wake, while this energy was sufficient to drive a high-amplitude wake of the right shape to produce an energetic, collimated electron beam. Continuing research is aimed at increasing electron energy even further, increasing the number of electrons captured and accelerated, and developing applications of the compact, multi-GeV accelerator as a coherent, hard x-ray source for materials science, biomedical imaging and homeland security applications. The second major advance under this project was to develop new methods of visualizing the laser-driven plasma wake structures that underlie laser-plasma accelerators. Visualizing these structures is essential to understanding, optimizing and scaling laser-plasma accelerators. Yet prior to work under this project, computer simulations based on estimated initial conditions were the sole source of detailed knowledge of the complex, evolving internal structure of laser-driven plasma wakes. In this project we developed and demonstrated a suite of optical visualization methods based on well-known methods such as holography, streak cameras, and coherence tomography, but adapted to the ultrafast, light-speed, microscopic world of laser-driven plasma wakes. Our methods output images of laser-driven plasma structures in a single laser shot. We first reported snapshots of low-amplitude laser wakes in Nature Physics in 2006. We subsequently reported images of high-amplitude laser-driven plasma "bubbles", which are important for producing electron beams with low energy spread, in Physical Review Letters in 2010. More recently, we have figured out how to image laser-driven structures that change shape while propagating in a single laser shot. The latter techniques, which use t ...
Author: Mianzhen Mo Publisher: ISBN: Category : Electrons Languages : en Pages : 283
Book Description
Ultra-intense (> 10^18 W/cm^2) laser interaction with matter is capable of producing relativistic electrons which have a variety of applications in scientific and medical research. Knowledge of various aspects of these hot electrons is important in harnessing them for various applications. Of particular interest for this thesis is the investigation of hot electrons generated in the areas of Laser Wakefield Acceleration (LWFA) and Fast Ignition (FI). LWFA is a physical process in which electrons are accelerated by the strong longitudinal electrostatic fields that are formed inside the plasma cavities or wakes produced by the propagation of an ultra-intense laser pulse through an under-dense plasma. The accelerating E-fields inside the cavities are 1000 times higher than those of conventional particle accelerators and can accelerate electrons to the relativistic regime in a very short distance, on the order of a few millimeters. In addition, Betatron X-ray radiation can be produced from LWFA as a result of the transverse oscillations of the relativistic electrons inside the laser wakefield driven cavity. The pulse duration of Betatron radiation can be as short as a few femtoseconds, making it an ideal probe for measuring physical phenomena taking place on the time scale of femtoseconds. Experimental research on the electron acceleration of the LWFA has been conducted in this thesis and has led to the generation of mono-energetic electron bunches with peak energies ranging from a few hundreds of MeV to 1 GeV. In addition, the Betatron radiation emitted from LWFA was successfully characterized based on a technique of reflection off a grazing incidence mirror. Furthermore, we have developed a Betatron X-ray probe beamline based on the technique of K-shell absorption spectroscopy to directly measure the temporal evolution of the ionization states of warm dense aluminum. With this, we have achieved for the first time direct measurements of the ionization states of warm dense aluminum using Betatron X-ray radiation probing. Fast Ignition (FI) is an advanced scheme for inertial confinement fusion (ICF), in which the fuel ignition process is decoupled from its compression. Comparing with the conventional central hot-spot scheme for ICF, FI has the advantages of lower ignition threshold and higher gain. The success of FI relies on efficient energy coupling from the heating laser pulse to the hot electrons and subsequent transport of their energy to the compressed fuel. As a secondary part of this thesis, the transport of hot electrons in overdense plasma relevant to FI was studied. In particular, the effect of resistive layers within the target on the hot electron divergence and absorption was investigated. Experimental measurements were carried out and compared to simulations indicating minimal effect on the beam divergence but some attenuation through higher atomic number intermediate layers was observed.
Author: Pierre Michel Publisher: Springer Nature ISBN: 3031234243 Category : Science Languages : en Pages : 423
Book Description
This textbook provides a comprehensive introduction to the physics of laser-plasma interactions (LPI), based on a graduate course taught by the author. The emphasis is on high-energy-density physics (HEDP) and inertial confinement fusion (ICF), with a comprehensive description of the propagation, absorption, nonlinear effects and parametric instabilities of high energy lasers in plasmas. The recent demonstration of a burning plasma on the verge of nuclear fusion ignition at the National Ignition Facility in Livermore, California, has marked the beginning of a new era of ICF and fusion research. These new developments make LPI more relevant than ever, and the resulting influx of new scientists necessitates new pedagogical material on the subject. In contrast to the classical textbooks on LPI, this book provides a complete description of all wave-coupling instabilities in unmagnetized plasmas in the kinetic as well as fluid pictures, and includes a comprehensive description of the optical smoothing techniques used on high-power lasers and their impact on laser-plasma instabilities. It summarizes all the key developments from the 1970s to the present day in view of the current state of LPI and ICF research; it provides a derivation of the key LPI metrics and formulas from first principles, and connects the theory to experimental observables. With exercises and plenty of illustrations, this book is ideal as a textbook for a course on laser-plasma interactions or as a supplementary text for graduate introductory plasma physics course. Students and researchers will also find it to be an invaluable reference and self-study resource.
Author: National Research Council Publisher: National Academies Press ISBN: 030908637X Category : Science Languages : en Pages : 177
Book Description
Recent scientific and technical advances have made it possible to create matter in the laboratory under conditions relevant to astrophysical systems such as supernovae and black holes. These advances will also benefit inertial confinement fusion research and the nation's nuclear weapon's program. The report describes the major research facilities on which such high energy density conditions can be achieved and lists a number of key scientific questions about high energy density physics that can be addressed by this research. Several recommendations are presented that would facilitate the development of a comprehensive strategy for realizing these research opportunities.
Author: Satomi Shiraishi Publisher: Springer ISBN: 3319085697 Category : Science Languages : en Pages : 133
Book Description
This thesis establishes an exciting new beginning for Laser Plasma Accelerators (LPAs) to further develop toward the next generation of compact high energy accelerators. Design, installation and commissioning of a new experimental setup at LBNL played an important role and are detailed through three critical components: e-beam production, reflection of laser pulses with a plasma mirror and large wake excitation below electron injection threshold. Pulses from a 40 TW peak power laser system were split into a 25 TW pulse and a 15 TW pulse. The first pulse was used for e-beam production in the first module and the second pulse was used for wake excitation in the second module to post-accelerate the e-beam. As a result, reliable e-beam production and efficient wake excitation necessary for the staged acceleration were independently demonstrated. These experiments have laid the foundation for future staging experiments at the 40 TW peak power level.
Author: Oliver Brning Publisher: World Scientific ISBN: 9814436402 Category : Science Languages : en Pages : 855
Book Description
"The past 100 years of accelerator-based research have led the field from first insights into the structure of atoms to the development and confirmation of the Standard Model of physics. Accelerators have been a key tool in developing our understanding of the elementary particles and the forces that govern their interactions. This book describes the past 100 years of accelerator development with a special focus on the technological advancements in the field, the connection of the various accelerator projects to key developments and discoveries in the Standard Model, how accelerator technologies open the door to other applications in medicine and industry, and finally presents an outlook of future accelerator projects for the coming decades."--Provided by publisher.
Author: Publisher: ISBN: Category : Languages : en Pages : 14
Book Description
Recently there has been a great interest in laser-plasma accelerators as possible next-generation particle accelerators because of their potential for ultra high accelerating gradients and compact size compared with conventional accelerators. It is known that the laser pulse is capable of exciting a plasma wave propagating at a phase velocity close to the velocity of light by means of beating two-frequency lasers or an ultra short laser pulse. These schemes came to be known as the Beat Wave Accelerator (BWA) for beating lasers or as the Laser Wakefield Accelerator (LWFA) for a short pulse laser. In this paper, the principle of laser wakefield particle acceleration has been tested by the Nd:glass laser system providing a short pulse with a power of 10 TW and a duration of 1 ps. Electrons accelerated up to 18 MeV/c have been observed by injecting 1 MeV/c electrons emitted from a solid target by an intense laser impact. The accelerating field gradient of 30 GeV/m is inferred.
Author: Grace Gloria Manahan Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Laser wakefield acceleration (LWFA) can occur when the ponderomotive force of high power ultra short laser pulses produce wakefields in underdense plasma. The structure of these wakefields are similar to those in rf cavities of conventional linear accelerators, but are characterised by large fields that can accelerate particles to high energies over much shorter distances. Compactness and inherent short bunch duration make LWFAs potential candidates for laboratory-scale coherent radiation sources. Currently, theoretical and experimental studies are being pursued to obtain in-depth understanding of LWFAs, in particular the injection mechanisms, as these will lead to better control and improved quality of the electron beams. Experimental effort is being directed towards the design of suitable diagnostics to measure the most important properties of the electron beam, one of which is the emittance. Emittance is a good figure of merit as it describes the beam distribution in phase space and provides information on the beam focusability. This work presents a numerical and experimental study of the potential of LWFA as a next generation table-top accelerator. The first part of the thesis investigates the transport of LWFA produced electron beams using conventional devices. To provide a "usable" beam, the transport system should be capable of preserving the transverse emittance. Possible sources of emittance growth are examined, focusing on the effects of energy spread, divergence and pointing stability on the emittance. The second part of the thesis presents direct single shot measurements of the transverse emittance using the pepper-pot technique. This method is also used to quantify the performance of high-gradient miniature permanent quadrupoles.
Author: Constantin Aniculaesei
Author: Karl Schmid
Author: 
Author: Mianzhen Mo
Author: Pierre Michel
Author: National Research Council
Author: Satomi Shiraishi
Author: Oliver Brning
Author: 
Author: Grace Gloria Manahan